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gunrunnerjohn:  “This is the TVS I use generally for train transformer voltages: 1500W 33.3V TVS at Digikey

texgeekboy: “…Would they be okay?  …..1.5KE36CA TVS Diodes 30.8V 1500W”

gunrunnerjohn:  “They should be fine.  If you were running MTH stuff with 24 volts from the early transformers, you might get into trouble, but not if you stick to the 19V maximum for TMCC/Legacy.”

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Okay, I am a bit confused.  Dale H way back when recommended the 36 volt TVS for PWZW with whistle button and new transformers like MTH's that go above 20+ volts.  The 33 volt TVS was good for Lionel's 18 volt bricks.  Therefore, the 1.5KE36CA texgeekboy bought should be good for MTH's transformers.  I either copied all that down wrong or something has changed.

John, didn't you use to recommend the 1.5KE36CA?

The peak voltage from the 24V MTH transformer is 1.414 times 24 or 33.936 volts.  The specifications for the 1.5KE36CA are...

Note that the minimum breakdown voltage is only 34.2, a bit too close to the voltage of the transformer.  So, some time back I elevated my thinking to give a slightly greater margin.

The specification of the 1.5KE39CA give a bit more leeway.

In most environments, you'd probably be fine with either.  However, if the voltage happens to sneak up where the TVS is conducting, it can quickly kill it.

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